1. Field of the Invention
Embodiments disclosed herein relate generally to the analysis and characterization of downhole fluid components.
2. Background Art
Hydrocarbons are found in subterranean formations. Production of such hydrocarbons is generally accomplished through the use of rotary drilling technology, which requires the drilling, completing and working over of wells penetrating producing formations.
During drilling operations, it is desirable to perform various evaluations of the subterranean formations penetrated by the wellbore. In some instances, the drilling tool may be removed from the wellbore and a wireline tool may be deployed into the wellbore to test and/or sample the formation. In other cases, the drilling tool may be provided with devices to test and/or sample the surrounding formation and the drilling tool may be used to perform the testing and/or sampling. These samples or tests may be used, for example, to locate valuable hydrocarbons.
Formation evaluation often requires that fluid from the formation be drawn into the downhole tool for testing and/or sampling. Various devices, such as probes, may be extended from the downhole tool to establish fluid communication with the formation surrounding the wellbore and to draw fluid into the downhole tool. A typical probe is a circular element extended from the downhole tool and positioned against the sidewall of the wellbore. A rubber packer at the end of the probe may be used to create a seal with the wall of the wellbore. Another device used to form a seal with the wellbore is referred to as a dual packer. With a dual packer, two elastomeric rings expand radially about the tool to isolate a portion of the wellbore therebetween. The rings form a seal with the wellbore wall and permit fluid to be drawn into the isolated portion of the wellbore and into an inlet in the downhole tool.
Conventional methods for performing quantitative analysis of the collected downhole fluid require the sample to be brought to the surface and subsequently analyzed in a laboratory environment. However, recent advances in material science and miniaturization technology have enabled real-time measurements of the collected downhole fluid components using downhole sensors. Moreover, several studies using downhole optical, magnetic resonance, sonic, and electrochemical modules have demonstrated the feasibility to conduct various fluid characterizations downhole with comparable quality of measurements to those conducted in a controlled environment (e.g., in a laboratory).
Standard analytical procedures are available to do quantitative analysis of the collected downhole fluid by addition of a reagent that reacts chemically with a target species in the fluid sample to cause detectible changes in fluid property, such as color, absorption, spectra, turbidity, etc. See Vogel, A. I., “Text-Book of Quantitative Inorganic Analysis, 3rd Edition,” Chapter 10-12, John Wiley, 1961. Such changes in fluid property may be caused, for example, by the formation of a product that absorbs light at a certain wavelength, or by the formation of an insoluble product that causes turbidity, or bubbles out as gas. For example, addition of organic, pH sensitive dyes is used for colorimetric pH determination of downhole water samples. Specifically, the organic dyes are stored in a sample bottle, injected to the flow line, and mixed with the sample at pump out module prior to measurement.
However, due to the high pressure and temperature conditions downhole, the organic materials used in the reagents are prone to chemical attacks. For example, in the case where the reagent includes a polymer based compound, chemical attacks from oxidation and/or free radicals often change the structure and characteristics of the polymer, resulting in changes of color, viscosity, and structure stability of the reagent. Furthermore, thermal oxidation and free radical attack may cause chain scission of the polymer because its main chain and/or side chain scission rates are accelerated at high temperature. Additionally, these chemical attacks may result in degradation of the downhole reagent thereby decreasing the quality of the sampled fluid. Furthermore, such degradation of the downhole reagent may reduce or even prevent the desired changes in fluid properties from occurring and thereby diminish the accuracy of the analytical procedures conducted downhole (e.g., due to loss of coloration of the reagent).
Accordingly, there exists a need for downhole reagents having improved chemical and thermal stability against chemical attacks from free radical and/or other oxidative species at high temperatures. Similarly, there exists a need for improved downhole fluid measurement methods that exhibit improved chemical and thermal stability when subjected to downhole pressures and temperatures.